Electronic calendar display devices suitable for timepieces and capable of displaying a full calendar month, where Sunday always appears in the leftmost displayed column, are known. An example of such a device is U.S. Pat. No. 4,353,178, issued on Oct. 12, 1982 and assigned to Kabushiki Kaisha Suwa Seikosha. The '178 patent discloses a liquid crystal display device which has two transparent baseplates stacked in alignment, with a liquid crystal material sandwiched in between. Six rows, 1-6, and ten columns, a-j, of electrodes are formed on each baseplate, as shown in FIGS. 1a and 1b. The overlapped electrode groups for display of dates are organized so that each row indicates a week. The first overlapped electrode row 1 has seven consecutive numerals, 1 to 7, starting at the fourth column d. The second overlapped electrode row 2 includes ten consecutive numerals, 5 to 14. The sixth row 6 includes nine consecutive numerals, 23 to 31. The third 3, fourth 4 and fifth 5 rows each include ten numerals; however, the electrode patterns at some positions are divided into small electrode segments such that more than one electrode segment is required to form a digit and more than one numeral can be formed at a given position on the display panel by selective driving of electrode segments. More particularly, in row 3, in the tens digit, the numeral 2 can be changed to the numeral 1 and vice versa. This construction applies in columns i and j. In row 4, there can be an interchange in displaying 2 or 1 for the tens portion of the date numeral, depending upon the electrodes which are driven, and this construction is applied in every column except column a. In the fifth row 5, certain tens digits can be either 3 or 2, and certain tens digits can be 2 or 1. This construction applies to rows a through i. The electrodes are driven by a V-2 V AC amplitude selective multiplexed system.
Depending upon the month which is to be displayed, either rows 1 through 5 are used or rows 2 through 6 are used. Then, generally seven columns are selected from the ten available columns a-j to be driven to display a month. The columns are selected in correspondence with the first day of the month.
The primary drawback of the '178 patent is its employment of electrode segments for certain tens digits. Although electrode segments do not pose problems for large numbers, segmenting small numbers, such as would be used for a calendar display in a watch, presents two difficulties. First, segmenting small numbers makes them difficult to read. Second, and perhaps of greater significance, is the technical feasibility problem posed by the more complex multiplexing scheme required for the segmented tens digits of small numbers.
Another approach in the construction of a full calendar month display for a timepiece is shown in FIG. 2. The display panel has thirteen columns of date numerals; however, on any given month, the date numerals are visibly displayed in only seven consecutive columns. Thus, there is a surplus of six columns which are not visibly displayed. This leads to an unbalanced display configuration for some calendar months as illustrated in FIGS. 2a and 2b, and the portion of the display panel driven for display is small and difficult to see and read, since thirteen full-width columns are required to display all of the months.
Accordingly, it is one object of the present invention to provide an improved liquid crystal calendar device, especially suitable for an electronic timepiece, capable of displaying a full calendar month with Sunday being in the leftmost displayed column.
Another object of this invention is to provide an improved liquid crystal calendar device where the date numerals are legible even when occupying a small area.
A further object of this invention is to provide an improved liquid crystal calendar device having a balanced display configuration with a simple multiplexing scheme.
Still another object of this invention is to provide an improved liquid crystal calendar device wherein the area occupied by the date numerals is reduced by interleaving the date numerals.